How to obtain output from instrument callback function?

Is it possible to get output from an instrument callback function in Matlab? I am reading data being sent to the serial port and a callback function is triggered when 1 byte becomes available

 s=serial('COM3');
 set(s,'BytesAvailableFcn',{@mycallback});
 set(s,'BytesAvailableFcnCount',1);
 set(s,'BytesAvailableFcnMode','byte');

I would like to record the exact time at which each callback occurs in a vector T. I am able to write the callback function such that I get a vector T, but I don't know to access T and it is not produced after the script has finished executing.

I could also have this vector T to be generated in the main script but I am unsure how to set the condition if the callback occurs. I previously thought that I could use bytes=get(s,'BytesAvailable') and if bytes==1 I could have the time recorded in the vector. But bytes have value = 1 only once and then continues to grow.

I am aware that there is a function record which could automatically record the callback information:

 s.RecordMode = 'append';
 s.RecordDetail = 'verbose';
 s.RecordName = 'test.txt';
 record(s)

However whenever I try this, it does not record as I want it to. Although I set s.RecordDetail to verbose, the output in the .txt is the same if I had not set the RecordDetail. In addition, I prefer to write to a vector/array rather than a file as it is faster.

Does anybody have any suggestions for this?

Thanks

Answer 1

[Walter Roberson]

I have not researched how Record mode works.

With respect to returning a value from the callback: No. Very few callbacks can return a value. The callbacks that can return values are concerned with filtering roi resize changes, or for generating custom text for datatips. None of the I/O or graphical object callbacks can return values.

http://matlab.wikia.com/wiki/FAQ#How_can_I_share_data_between_callback_functions_in_my_GUI.3F

[Maheen Siddiqui]

Thanks for this! Thats very useful. After I wrote this post, it did occur to me that I could try to make the variable global and see if that works. But it also seems like I could save the variable to a mat file and then I will have access to it.